1. Field of the Invention
The present invention relates generally to medical apparatus and methods. More particularly, the present invention relates to implantable devices and methods and systems for detecting their malfunction or failure or impending malfunction or failure.
All implants of devices, especially those indicated for long term use, in the human body are highly regulated and must meet certain safety requirements. One such requirement is biocompatibility of the materials used in the construction of the device in the event they come into direct contact with body tissues and fluids. Even if the material is biocompatible, the contact with body tissues and fluid could result in diminished performance or malfunction esp. in devices with electronic components. It is known that when a device is implanted in the body, the materials forming the cover and structural elements of the device degrade and fatigue over time. It is also well known that excessive handling during implantation or even normal, repetitive movements could stress the structural integrity of the device. Failure of the structural integrity of the device or its covering, which eventually happens, causes the contents of the device, which heretofore were confined in the interior of the device, to be in contact with the surrounding tissues and their secretions. Therefore, it would be desirable to detect or to predict such an event before any potentially harmful contents come in contact with the surrounding tissues, before tissue secretions leak into the interior of the device resulting in malfunction, or before the content itself suffers a malfunction.
Prosthetic devices implanted in numerous locations in the body are prevalent in medical practice. Many of these prostheses are designed to assume the structural shape of the body part yet are soft and have similar flexibility to approximate the look and feel of normal human tissue. A common use has been for reconstructing the normal contour, improving the shape, and/or enlarging the size of the human breast. The most common breast prosthesis is a soft elastomeric container made of silicone rubber which is filled or “inflated” with a liquid or gel, typically a saline solution or a silicone gel, or a combination of such filling materials. Typically such prostheses are surgically implanted to fit underneath the skin of the body either between the chest wall and the mammary gland or in place of the mammary gland following a mastectomy. The ideal result after implantation is to achieve the contours and tissue characteristics of a natural breast, and prosthetic devices filled with silicone gel have been found to produce the best cosmetic result. Hence, silicone gel breast implants are the devices of choice in locations where they are approved.
Degradation and fatigue of the silicone rubber container of such breast implants, however, can lead to perforations, tears, ruptures, and seam separations, resulting in the leakage of filling materials to the surrounding tissues. Leakage from a saline filled device is usually harmless as the solution, if uncontaminated, is absorbed. Leakage from the preferred silicone gel filled device is much more problematic. Bleeding of gel at the surface is believed to contribute to the development of capsular contracture, a scarring condition that compresses the implanted device from a soft, natural profile into a rigid, spherical shape. More serious is the migration of leaked silicone gel to other parts of the body such as the lymph nodes and major organs where it becomes unremovable. Consequently, silicone gel has been implicated in many health problems including connective tissue diseases. This risk increases with the length of time the device is implanted.
The problem is exacerbated by the fact that leakage of silicone gel is not easily detected and the rupture of the device cannot be predicted. Unlike saline filled devices where rupture and leakage results in deflation over a short period of time and readily discovered by the patient, silicone gel tends to leak slowly and can go unnoticed for years. Often the rupture is discovered only upon removal of the device for another reason. The only noninvasive method currently sensitive enough to detect such an event reliably is an MRI scan. To monitor the integrity of a silicone gel device by regularly scheduled MRI scans is cost prohibitive. Consequently, the use of silicone gel filled breast prostheses is now highly restricted by regulatory authorities.
Gastric balloons are another type of implantable, inflatable prosthesis which is subject to failure from breach of the wall. Gastric balloons are typically introduced through the esophagus and inflated in situ in order to occupy a significant volume within the stomach. While gastric balloons are typically inflated with saline or other non-toxic materials which are benign if released into the stomach, the balloon structure itself is hazardous if accidentally deflated since it can pass and cause obstruction of the pyloric valve or the intestines distal to the pyloric valve. Any such obstruction is a medical emergency.
The problem is not limited to inflatable devices. Many implanted devices, e.g., cardiac pacemakers, contain electronic circuits and have insulated wires or leads that sense or deliver signals at certain points in the body. For example, the covering or insulation could deteriorate over time or tear in response to normal body movements. Body fluids from the surrounding could then leak into the circuitry, either as a liquid or vapor, causing disruption of signals. Or the lead could break at any point or detach from the connector to the device. Another class of implanted devices involves a closed vessel system conveying fluids leading from a part of the device or a part of the body to another part of the body, such as a shunt conveying blood or cerebrospinal fluid. The catheter or reservoir in the system could tear or break leading to the leakage of material out of the catheter to an unintended part of the body or leakage of body fluids into the catheter causing contamination. Yet another class of devices, which depend on solid objects for function or structural support, could fail from fracture or dislocation. These fractures can start as a hairline from repeated mechanical stress from use and progress to a complete fracture. Dislocations start with a loosening of the structure(s) holding an object in place and progress to a complete dislocation.
For these reasons, it would be desirable to provide apparatus and methods to detect or predict an actual or potential wall breach which can lead to leakage of the filling contents of breast implants, gastric balloons, catheters, reservoirs, and the like or an actual or potential disruption of an electronic circuit in cardiac pacemakers or neurostimulators or the like or an actual or potential stress fracture or dislocation in the case of solid components in prosthetic devices or the like. It would desirable further to monitor remotely the structural integrity and presumed functional status of a device without activating the function after device implantation in the case of cardiac defibrillators or without directly applying stress to the monitored part in the case of solid components. Prompt removal of such devices upon breach or imminent breach would avert most, if not all, of the ensuing problems including catastrophes. The methods and apparatus will preferably be adaptable for use in any structural design of the device without adversely affecting its structure or, in the case of breast implants, the final cosmetic result, and further be applicable to solid and rigid body implants containing electronic components such as pacemaker and defibrillator canisters and leads and to solid body implants such as prosthetic heart valves or orthopedic devices. It would be further desirable if the breach or imminent breach of the device were detectable to the patient in an easy, rapid, and reliable fashion outside of a medical facility or at home. Additionally, it would be beneficial if the system were able to monitor the device non-invasively on a frequent basis over the life of the device without incurring significant additional cost for each diagnostic event. At least some of these objectives will be met by the inventions described hereinafter.
2. Description of the Background Art
Leakage detection is described in U.S. Pat. No. 6,826,948 and published applications US 2004/0122526 and US 2004/0122527. Breast implants and methods for their use are described in U.S. Pat. Nos. 6,755,861; 5,383,929; 4,790,848; 4,773,909; 4,651,717; 4,472,226; and 3,934,274; and in U.S. PubL Appln. 2003/163197. Gastric balloons and methods for their use in treating obesity are described in U.S. Pat. Nos. 6,746,460; 6,736,793; 6,733,512; 6,656,194; 6,579,301; 6,454,785; 5,993,473; 5,259,399; 5,234,454; 5,084,061; 4,908,011; 4,899,747; 4,739,758; 4,723,893; 4,694,827; 4,648,383; 4,607,618; 4,501,264; 4,485,805; 4,416,267; 4,246,893; 4,133,315; 3,055,371; and 3,046,988 and in the following publications: US 2005/0137636; US 2004/0215300; US 2004/0186503; US 2004/0186502; US 2004/0162593; US 2004/0106899; US 2004/0059289; US 2003/0171768; US 2002/0099430; US 2002/0055757; WO 03/095015; WO88/00027; WO87/00034; WO83/02888; EP 0103481; EP0246999; GB2090747; and GB2139902.